Color Gamut Volume Research Articles

8‐1: Riemannian Color Difference Metric

We developed a new Riemannian color difference metric based on Friele's line element and the results of psychophysical color discrimination experiments. Visual adaptation effects are incorporated into the model. This new color difference metric was validated against various data sets available in the literature. We found adequate agreement with experimentally determined threshold ellipsoids/ellipses and a better threshold predictability compared with other color difference metrics. The new Riemannian color difference metric was applied for the calculation of the color gamut volume and the maximum number of mutually discernible colors.

Starch‐based nanoparticles as a replacement for synthetic latex: A comprehensive assessment of printability and colorimetric characteristics

AbstractThe papermaking, packaging, and printing industry are actively seeking sustainable material alternatives to address growing concerns about environmental consciousness and finite resources. Synthetic latex, a frequently utilized binder in paper coating formulations, present difficulties due to their dependence on fossil fuel resources and their reduced recyclability in comparison to eco‐friendly sustainable products. In this study, synthetic latex was replaced with a starch‐based nanoparticle (starch NP) binder at a 1:1 ratio in a coating formulation. Printing trials to assess colorimetric characteristics was made using electrophotography (EP) printing, given the current upward trajectory and expansion of EP technology into the label, packaging, and folding carton sectors. The in‐depth investigations reveal that incorporating starch NP binder result in improved optical, color, and dot characteristics. Moreover, it maintains consistent and comparable coefficients of friction. Partial replacement of synthetic latex with the starch NP binder yields significant enhancements in surface roughness and text quality. Importantly, the starch NP binder not only improves the dielectric relaxation properties of the paper and enhances toner transfer but also accelerates the distribution of the electrical field compared to synthetic latex, optimizing toner transfer and thereby enhancing color gamut volume. The study demonstrates that employing the starch NP binder leads to substantial improvements in colorimetric performance without any drawbacks in EP printing, making it highly advantageous to replace 50% of the synthetic binder.

Addition of fibers derived from paper mill sludge in paper coatings: impact on microstructure, surface and optical properties

Traditionally, cellulose nanofiber (CNF) production has primarily relied on virgin cellulose sources. Yet, the shift to using paper mill sludge (PMS) as a source for CNF underscores the significance of reusing and recycling industrial byproducts. PMS contains significant amounts of cellulose that can be extracted as a raw material. The purpose of present study is to provide a sustainable approach to PMS utilization as a paper coating additive in the cellulose nanofibrils (CNFPMS) form via simply scalable wire-wound rod coating method. The effect of CNFPMS additive amounts at two coating layers on microstructure and surface properties of coatings such as porosity, air permeability surface roughness and optical properties such as brightness, gloss and CIE L*a*b* is studied, which they can also provide insight for the eventual print performance. Results indicated that the obtained CNFPMS in paper coating shows 52% decrease in porosity, presenting significant improvement in the coating microstructure. The marginal increase in permeability coefficient and surface roughness, 54% and 10%, respectively, suggests improving color reproduction and preventing color density losses. Optical analysis showed slight decrease in brightness and gloss, as was expected. Notably, the lightness was improved, which also indicates increasing color gamut volume in printing applications. As a result, the current work offers a sustainable approach to manage PMS for use in paper coatings as a high-value-added material.

Color gamut volume and the maximum number of mutually discernible colors based on a Riemannian metric.

For the calculation of the color gamut volume and the maximum number of mutually discernible colors, an algorithm based on a Riemannian metric and the densest packing of spheres is proposed. With this algorithm, the color gamut volume was calculated for the conditions of experiments reported in literature. Good agreement was found with the experimental findings of the color gamut volume as a function of the peak luminance. Using the new algorithm, the color gamut volume and the maximum number of mutually discernible colors was calculated for various sets of primary colors corresponding to display standards and various dynamic ranges. Comparisons were made with state-of-the-art methods which are based on the Euclidean metric in approximately uniform color spaces and a simple cubic lattice. It was found that the state-of-the-art methods underestimate the maximum number of mutually discernible colors. However, the relative differences decrease as the primary colors are more saturated. Based on the new algorithm the maximum number of mutually discernible colors was calculated for a range of peak retinal illuminance levels and various sets of primary colors. We found that, for a given set of primary colors, the maximum number of mutually discernible colors is proportional to the logarithm of the ratio of the peak retinal illuminance level and a fitting parameter.

Research on the color gamut volume and light efficiency in four-primary laser display systems.

The color gamut volume (CGV) and light efficiency of a four-primary display system were theoretically simulated with different wavelength configuration. Given the wavelengths of the blue and red primaries, we optimized the other two primary colors; the wavelength set with the largest CGV was chosen. The maximum CGV, 2.346 × 106, was obtained at (660, 530, 507, 465) nm. The maximum light efficiency was also determined. A trade-off between CGV and light efficiency should be made according to the requirement of the devices. This study provides guidance for the construction of a four-primary laser display system and the optimization of the CGV in multi-primary display systems.

18‐3: Computing Display Color Gamut Volume using Tetrahedra

We describes an approach to computation of display color gamut volume (sometimes called color volume). We describe two methods of partitioning color space into tetrahedra, and methods of aggregating the volume of tetrahedra. There some mathematical subtleties that need to be addressed to efficiently obtain the correct result. We discuss the constraints that guide a suitable choice of color space in which to perform the calculation. Our goal is to characterize the range of physical stimuli produced by a display. We want a perceptual measure of this volume, but we want the metric to cover the entire range of physical display stimuli, not just the range attained at a particular state of the viewer's adaptation. We comment on using CIE LAB or BT.2124 ITP5 as the underlying colorspace, and suggest that ITP is most useful.

Potential application of a green fiber laser in laser display systems.

This study explores the application of optical fiber lasers in display systems by integrating a P r3+-doped green all-fiber laser into a laser projection display system. As a control group to compare the results, a 520nm semiconductor green laser diode module was integrated, similar to the experimental group. The color gamut and speckle performances were studied and compared. The results showed that the experimental group performed slightly better in the color gamut volume. The speckle contrast decreased rapidly in the experimental group when power increased. To our knowledge, this is the first study to apply a fiber laser to a laser display system. The results shed light on developing laser display systems with fewer or no speckle reduction elements.

Evaluation of gamut enhancement in yellow regions and a choice of optimal wavelength for a RGBY four-primary laser display system.

To improve the color rendering ability in yellow color regions, the inclusion of yellow among the primary colors is commonly proposed. In this study, an algorithm for evaluating gamut enhancement in yellow regions is developed. The performance of different wavelength sets of RGBY four-primary system is studied theoretically in terms of various aspects, including the color gamut volume, gamut coverages, and gamut enhancement ratio in yellow regions. The optimal wavelength set and its optimal luminance ratio are then determined. This research provides strong guidance for the construction of practical four-primary-laser display systems.

Upper limit of gamut volumes in multi-primary display systems.

Based on the difference between multi-primary displays (MPDs) and three-primary displays, we propose a new definition for evaluating the color gamut volume (CGV) to explore the upper limit of MPDs, which could theoretically represent all colors that MPDs can display. The proposed definition corrects the defects in the L*a*b* color space that arise when calculating the CGV of MPDs. In view of the high computational complexity of this method, we propose a simplified scheme with a small margin of error. Additionally, we verify the new definition with experiments on a six-primary projector. This method is helpful in guiding the selection of light sources and the evaluation of MPDs, and also has great reference value to calculate the target gamut for gamut mapping in MPDs.

Perceived Color Gamut in Images: From Boundary to Difference.

A larger display color gamut volume (CGV) is expected to produce higher perceived brightness and colorfulness of the images displayed. However, display control algorithms such as gamut mapping and color conversion need to be carefully controlled to fully take advantage of the higher luminance and more saturated display primaries. Using RGBW displays (RGB plus a white channel) as a special case in contrast to RGB displays, it is demonstrated that a larger RGB display gamut enclosed by the boundary did not guarantee a larger color gamut perceived in images. Five gamuts with different white channel contributions were simulated, and seven different image contents were curated and rendered on each display. Using a paired comparison experiment with 33 observers, the perceived scales of color gamut as perceived brightness and colorfulness were derived. The results show more correlation with the image-wise than display-wise CGV and can be explained with image color differences. Our findings highlight the importance of considering image contents when optimizing display gamut volume, which can be guided by such image-wise analysis.

23‐1: Invited Paper: Visualization of Color‐Gamut Coverage‐Gamut Ring Intersection

The D50 CIELAB gamut volume was standardized as a suitable and unified gamut size measurement methodology. The color gamut volume is visualized using proportionate gamut rings in a two‐dimensional diagram. Gamut ring intersection assists the visual comparison of the size and shape of the color gamut coverage between a display and a reference. This paper introduces a desktop application with an intuitive graphical interface for visualizing the gamut rings and describes the algorithm of the gamut ring intersection.

Impact of color temperature on the color gamut volume of a six-primary-laser display system

ObjectiveColor temperature (CT) is closely related to the color gamut of a display system. It is important to investigate how the color gamut volume and gamut coverage vary with the CT. MethodsThe effects of the CT on gamut volume and coverage in a six-primary-laser display system (in which color was achieved through a fixed mixture of two sets of three-primary) were investigated, both theoretically and experimentally. ResultsThe results indicated that the gamut volume increased rapidly from 64.19% to 139.99% Rec. 2020 when the CT increased from 2000 K to 12,500 K and then increased gradually to 142.4% at 20,000 K. The gamut coverage first increased to the maximum at 5000 K and then decreased. At 5000 K, the gamut volume was moderate, but the gamut coverage was the highest. Between 10,000 and 12,500 K, the gamut volume increased significantly, and the gamut coverage remained relatively high. At 20,000 K, the gamut volume was the largest, whereas the gamut coverage was relatively low. Accordingly, in the six-primary-laser display system, from the perspectives of improved gamut coverage and color management, D50 could be a safer recommendation; for better rendering ability, the CTs between 10,000 K and 12,500 K could be adopted.

General solution to the calculation of peak luminance of primaries in multi-primary display systems.

For a display system, a wide-color gamut can significantly improve the viewing experience. It is known that an ultra-wide color gamut can be achieved using more primaries. However, for multi-primary displays (MPDs), choosing the parameters of the primaries (e.g., wavelength and luminance) is not trivial because the necessary theoretical foundation is still lacking. In this study, starting from three-primary display, we proposed a method for calculating all possible peak luminances of MPDs. This is done by mathematically representing the added new primaries with the original three primaries. Of all the possible results, by optimizing the peak luminance of each primary color, the theoretical gamut volume satisfying specific requirements could be obtained. The method provided can be extended to N primaries (N > 6). Using this method, we have successfully built a six-primary display system and used it to verify the validity of the method. Combined with the calculation of color gamut volume, the theoretical framework provided can be used to guide the selection of wavelength, spectrum width, and luminances of primaries in MPDs.

Proper application of chromaticity gamut area metrics for displays.

The areal dimension in chromaticity diagrams is often used to evaluate the range of reproducible colors (or color gamut) of a display; however, its meaning is not fully understood. For consistent and meaningful color gamut comparisons, the metric needs a color space with a common chromatically adapted white point, which is not considered in legacy chromaticity gamut area metrics. This study demonstrates the validity of chromaticity gamut area metrics and clarifies the proper way to use the metrics by comparing the color gamuts of synthetic additive displays with a range of sampled RGB primaries with different white points. The study reports high correlations of 0.98-0.99 between the xy chromaticity gamut area and color gamut volume for additive displays with a common white point at 6500 K and above. However, using the "gamut rings" 2D visualization method, this study also demonstrates that use of different white points cause a failure of the chromaticity gamut area metric.

Expanding the color gamut of inkjet textile printing during color matching

AbstractOne of the most important subjects of digital printing is evaluation of color gamut mapping. A printer can only reproduce colors that are in its color gamut. Maybe, a color tolerance between reference sample and printed sample is in agreement between manufacturer and customer. The goal of this work is to estimate the expansion of the color gamut of an inkjet textile printer by consideration of the acceptable (predetermined) color difference during color matching. For analyzing the color gamut, a standard color chart IT8.7/4‐2005 CMYK target was printed by nine different mixtures of CMYK, and then the reflectance spectra and colorimetric parameters of the printed samples were measured. The inks used were disperse water‐based inks that were printed on the polyester fabric. The maximum acceptable color difference in this study was equal to 2 CIELAB units for all colors. In order to estimate the color gamut with the maximum acceptable color difference, for all boundary points of gamut, expanded points were obtained by Euclidean distance less than = 2. The results show that when the acceptable color difference is considered in color gamut measuring, the area and volume of the color gamut are increased and so, the reproducibility of printer is increased. The maximum and minimum expansions of color gamut volumes were obtained by the mixtures with minimum and maximum color gamuts, respectively. The volume expansion of the mixture with the minimum color gamut volume was 34.20%, while the volume expansion of the mixture with the maximum color gamut volume was 28.06%.

25.1: Invited Paper: Evaluation and standardization of light output and color gamut volume for laser projection displays

Laser projection displays have the advantage of light enhancement, color reproduction, luminance contrast, and dynamic range. Such projection displays are believed to produce images that look brighter and more vivid. The characterization and measurement of the displays' optical performance are important to measure the true performance of these displays. This paper introduced the evaluation of light output and color gamut volume for laser projection displays discussed in the IEC 62906‐5‐1 document.

Effect of Peak Luminance on Perceptual Color Gamut Volume

In this paper, two psychophysical experiments were conducted to explore the effect of peak luminance on the perceptual color gamut volume. The two experiments were designed with two different image data rendering methods: clipping the peak luminance and scaling the image luminance to display's peak luminance capability. The perceptual color gamut volume showed a close linear relationship to the log scale of peak luminance. The results were found not consistent with the computational 3D color appearance gamut volume from previous work. The difference was suspected to be caused by the different perspectives between the computational 3D color appearance gamut volume and the experimental color gamut volume/perceptual color gamut volume.

50‐2: Distinguished Paper: Measuring the Color Capability of Modern Display Systems

Historically displays used three colorants in an additive system. The CIE chromaticity diagram adequately illustrated color capability. Modern displays are not constrained by this additive architecture and the diagram can fail in its purpose. The “gamut rings” diagram provides a solution to illustrate color capability that directly correlates to color gamut volume.

Measuring the color capability of modern display systems

AbstractHistorically displays used three colorants in an additive system. During that time, the CIE chromaticity diagram adequately illustrated color capability. Modern displays are not constrained by this additive architecture, and the diagram can fail in its purpose. This is demonstrated by analysis and a large number of display measurements. A device‐independent methodology using CIE 1976 L*a*b* color gamut volume is described that provides a robust means to determine the size of the color gamut. This methodology is then extended to the ‘gamut rings’ diagram as a solution for visualizing color capability that directly correlates to color gamut volume. It is further shown how the methodology can be applied to determine the intersection between two gamut volume boundaries.

Spectral Optimization of White LED Based on Mesopic Luminance and Color Gamut Volume for Dim Lighting Conditions

The study aims to propose an approach of white LED spectral optimization based on mesopic luminance and color gamut volume for dim lighting conditions. Three optimal white LED spectra with relatively higher mesopic luminance and color gamut volume, the highest mesopic luminance, and the largest gamut volume are recommended for reducing energy consumption and enhancing color perception and recognition of human eyes. The theoretical simulation shows that the spectra with higher correlated color temperatures (CCT) and S/P-ratio increase the mesopic luminance and also extend the range of color gamut with the decreasing of lighting level. An evaluation model is developed to faster predict mesopic luminance, color gamut volume, and S/P ratio for lighting applications.